Update the annotation of layers.py

python/paddle/trainer_config_helpers/layers.py

@@ -921,7 +921,7 @@ def data_layer(name, size, depth=None, height=None, width=None,
 
         data = data_layer(name="input", size=1000)
 
-    :param name: The name of this layer. It is optional.
+    :param name: The name of this layer.
     :type name: basestring
     :param size: Size of this data layer.
     :type size: int